Arrangement for electrically connecting semiconductor circuit arrangements to an external contact device and method for producing the same

ABSTRACT

An electrical connection arrangement between a semiconductor circuit arrangement and an external contact device, and to a method for producing the connection arrangement is disclosed. In one embodiment, a metallic layer is deposited onto at least one contact terminal and/or the contacts and the wire, the metallic layer protecting the contact terminal or the electrical connection against ambient influences and ensuring a high reliability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Utility Patent Application claims priority to German PatentApplication No. DE 10 2005 028 951.7 filed on Jun. 22, 2005, which isincorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to an electrical connection arrangement between asemiconductor circuit arrangement and an external contact device, and toa method for producing a connection arrangement.

BACKGROUND

In the production of modules containing integrated circuits, orsurface-mountable components (SMD), usually the circuits and componentsare first produced on or in semiconductor wafers by means ofmicroelectronic technologies and circuit arrangements are thus formed,contact terminals for electrical connection to an external contactdevice being applied on the surface of the semiconductor circuitarrangement. The semiconductor circuit arrangements or semiconductorchips are then singulated, connected to external contact devices andenclosed by a housing. Within this process, the semiconductor circuitarrangements are electrically characterized and mounted on a carrier andthe electrical connection to external terminals is produced.

Contact terminals on the surface of semiconductor circuit arrangementsare subjected to various ambient influences during the processing, theelectrical characterization of the components and circuits contained andthe subsequent production of the electrical connection to an externalcontact device. Thus, by way of example, as a result of needle cardcompressions during the measuring operation or as a result of thebonding, cracks may arise in the metallization of the contact terminal,the cracks promoting diffusion of alkali metal ions, e.g. Na ions, intothe semiconductor circuit arrangement, specifically into the activeareas, and thus leading for example to a shift in the threshold voltageof transistors.

The electrical connections between a semiconductor circuit arrangementand an external contact device can be implemented in various ways. Onevery widespread method is wire bonding using an Au or Al wire. In thiscase, a first end of the wire is fixed on the internal contact terminalon the surface of the semiconductor circuit arrangement, the wire issubsequently led from there to an external contact terminal on thesurface of the external contact device and the second end of the wire isfixed on the external contact terminal.

Various methods which differ with regard to the materials used and theprocess parameters used, such as e.g. pressure and temperature, arecustomary in the case of wire bonding. Thermocompression bondinginvolves using an Au wire, the end of which is melted and pressed ontothe contact terminal. Ultrasonic bonding involves fixing an Al wire, forexample, on the contact terminal by means of a cold welding compressionconnection, that is to say at room temperature with application ofultrasound. A combination of both methods is also possible.

Producing the electrical connection by means of bonding entails someserious problems. During bonding on the surface of the semiconductorcircuit arrangement, it is possible, primarily in the case of processparameters which lead to a great deformation of the bond (overbonding),for cracks to occur in the contact metallization, the cracks promotingdiffusion of alkali metal ends, e.g. Na ions, into the active regions ofthe semiconductor circuit arrangement and thus leading to an alterationof the electrical properties of the semiconductor circuit arrangement.The bonding yield and the reliability of the bonding connections, e.g.the power cycling strength, are dependent on the process parameterschosen. Thus, a low pressure during the production of the bondingconnection may increase the yield, but it simultaneously reduces thereliability, whereas although an increased pressure during theproduction of the bonding connection and thus an enlarged bearing areaof the wire on the contact terminal increase the reliability, theynonetheless lead for example to the abovementioned problems with cracksin the metallization.

This problem is relevant particularly when using thick wires such as areemployed in the bonding of power semiconductor modules on account of thehigh current-carrying capacity acquired.

Furthermore, corrosive molding compound materials may attack the bondingcontact, which reduces the strength and reliability of the contact.These materials are part of the housing which encloses the semiconductorcircuit arrangement and the external contact device. Furthermore,portions of the bonding contact are observed to be etched away from thecontact terminal during subsequent processes on account of differentchemical potentials.

In order to solve these problems, complicated optimization processeshave been carried out hitherto for the electrical characterization bymeans of needle cards and for the bonding parameters, but although theyhave brought about an improvement, they do not constitute a finalsolution to the problem. Furthermore, the metallization on the surfaceof the semiconductor circuit arrangement has been embodied as a verythick layer or mechanically hardened by the targeted admixture ofadditional materials in order that process parameters which enable ahigh yield and reliability can be used during bonding. For mechanicalstabilization of the bonding contact on the surface of the semiconductorcircuit arrangement, which is necessary particularly in the case ofbonding processes without great deformation of the bonding wire, andalso protection against aggressive molding compound materials, a hard,high-temperature-resistant plastic is applied to the bonding contact.However, all these solution approaches lead to a significant increase incosts. There is currently no solution for the problem of the bondingcontact being etched away on account of different chemical potentials.

U.S. Pat. No. 6,825,564 discloses a method in which an NiP layer wasdeposited in electroless fashion on a contact terminal made of Cu inorder to prevent the oxidation of the Cu surface and thus to improve thebondability of the contact terminal.

U.S. Pat. No. 6,564,449 describes a method for reinforcing the contactterminal on the surface of the semiconductor circuit arrangement, inwhich an additional layer system made of Ti, Cr or TiW and Au or made ofNi and Au is deposited on the contact terminal in order to increase thereliability and reproducibility of the bonding contact in the case ofreverse wire bonding using Au wire.

DE 26 50 348 A1 describes a connection arrangement in which a layersystem comprising an Ni layer and an Au layer was applied to thepin-type electrical connecting conductors of a discrete electricalcomponent and to the conductor track to be connected thereto on aprinted circuit board, in order to improve the solderability of thecontact terminals.

A use of Cu as material for the wire is envisaged in the future onaccount of the good electrical properties of Cu. This is not yetpossible at the present time, however, since high forces are necessarywhen producing the contact between the Cu wire and the contact terminal,which, in the case of the present-day embodiment of the contactterminals on the surface of the semiconductor circuit arrangement, leadsto damage in the contact terminal and the underlying regions of thesemiconductor circuit arrangement.

For these and other reasons, there is a need for the present invention.

SUMMARY

The present invention provides an electrical connection arrangementbetween a semiconductor circuit arrangement and an external contactdevice, and to a method for producing the connection arrangement. In oneembodiment, a metallic layer is deposited onto at least one contactterminal and/or the contacts and the wire, the metallic layer protectingthe contact terminal or the electrical connection against ambientinfluences and ensuring a high reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification. The drawings illustrate theembodiments of the present invention and together with the descriptionserve to explain the principles of the invention. Other embodiments ofthe present invention and many of the intended advantages of the presentinvention will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 illustrates a schematic illustration of a conventional connectionarrangement.

FIGS. 2A to 2D illustrate schematic illustrations of a connectionarrangement in accordance with the present invention in particularlypreferred embodiments in each case.

FIGS. 3A to 3D illustrate schematic illustrations of a method inaccordance with the present invention in particularly preferredembodiments in each case, in flowcharts.

FIG. 4 illustrates a perspective illustration of a finished mountedsemiconductor circuit arrangement using the connection arrangementaccording to the invention.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments of the present invention can be positioned ina number of different orientations, the directional terminology is usedfor purposes of illustration and is in no way limiting. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the scope of thepresent invention. The following detailed description, therefore, is notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims.

The present invention provides a connection arrangement between asemiconductor circuit arrangement and an external contact device, inwhich a wire is used to produce the electrical connection between aninternal contact terminal on the surface of the semiconductor circuitarrangement and an external contact terminal on the surface of theexternal contact device, which connection arrangement is resistant toambient influences, ensures a stable, reliable electrical connection inconjunction with a high process yield and makes it possible to use Cu asmaterial for the wire. Furthermore, the invention provides a method forproducing such a connection arrangement.

In one embodiment of a connection arrangement of the type according tothe invention, an additional metallic layer is applied on at least theinternal contact terminal and on the wire or on the surface of at leastone contact terminal connected to the wire and the wire or on bothcontact terminals. In a further connection arrangement of the typeaccording to the invention, an additional metallic layer is applied onlyon the internal contact terminal, the diameter of the wire being atleast 500 μm or the wire comprising Cu. The diameter of the Cu wire isat least 50 μm for a thin wire and at least 300 μm for a thick wire.

The metallic layer protects the contact terminal against ambientinfluences during the electrical characterization and the furtherprocessing, in particular by virtue of the fact that cracks in themetallization that promote the diffusion of alkali metal ions areavoided or covered and, if appropriate, oxidation of the metallizationsurface is prevented. Furthermore, the metallic layer makes it possibleto use Cu as material for the wire and particularly favorable processparameters during the production of the electrical connection by meansof a wire, mechanically stabilizes the electrical connection and makesit resistant to chemical processes.

The connection arrangement according to the invention provides the highyield of the bonding process on account of the favorable processparameters that are possible and the high reliability of the electricalconnection, particular requirements made of the metallization on thesurface of the semiconductor circuit arrangement, such as e.g.mechanical hardness and/or large thickness, being obviated when usingthick Al or Au wires (diameter of at least 500 μm). Failures of theelectrical connection which result from fractures within the wire closeto the bonding contact such as occur in the case of bond coating with aplastic are also avoided. The metallic layer additionally acts as aprotective layer against etching and diffusion processes during furtherprocessing and during later use of the module containing a connectionarrangement. When the metallic layer is deposited on the wire, itprevents the corrosion of the wire and thus increases the reliability.

Furthermore, the present invention provides for the application of sucha metallic layer to other connection arrangements, too, in which theelectrical contact has been produced in a different manner, e.g. bysoldering.

The metallic layer includes arbitrary Ni compounds, in particular NiP,NiB, NiMo, NiRe or tertiary material compositions NiPX, where Xcomprises Cu, W, Sn, Mo or Sb. In this context, the designation NiY orNiPX denotes an Ni—Y or NiP—X alloy, respectively, that is to sayelemental Ni with an admixture of Y or P and X, respectively. As analternative, the metallic layer comprises Cu, Ag, Sn, SnAg or Au. Thelayer has a thickness of 0.1 to 100 μm, a typical thickness between 1 to5 μm. Advantages of NiP, NiB, NiMo, NiRe and the tertiary materialcompositions mentioned are the great hardness and the possibility ofbeing able to deposit these metals by means of an electroless method.The phosphorous content of 5 to 10% in NiP or the boron content of 1 to5% in NiB prevents the oxidation of the surface of the Ni layer. Afurther layer may be applied to the metallic layer, which further layercomprises Pd or Au and passivates the metallic layer and makes itchemically resistant and is advantageous for further processes. By wayof example, it prevents the oxidation of the surface of the metalliclayer and improves the bondability. Furthermore, a uniform coating ofthe connection arrangement with a noble metal is advantageous withregard to further processes and the reliability of the connectionarrangement. The layer comprising Pd or Au is thin in comparison withthe metallic layer, with a thickness of a few hundred nm.

The metallic layer or the layer system may be adapted to therequirements and conditions of the semiconductor circuit arrangement andof the external contact device and also of the process for producing theelectrical connection, in particular with regard to the materials usedand the process parameters of the deposition.

In one embodiment, it is additionally possible to effect furthermechanical stabilization of the electrical connection and protection ofthe bonding contact against attack by molding compound materials by theapplication of a hard, high-temperature-resistant plastic to the bondingcontact.

In one method according to the invention, the metallic layer is appliedafter producing the electrical connection between the semiconductorcircuit arrangement and the external contact device and thus envelops atleast one of the contact terminals connected to the wire and also thewire itself.

In another embodiment of the method according to the invention, themetallic layer is deposited prior to producing the electrical connectionto the external contact device. This may be done both in the waferassembly and on the already singulated semiconductor circuitarrangement, so that the metallic layer is situated only on the internalcontact terminal. If the metallic layer is not deposited until after thesemiconductor circuit arrangement has been mounted on a carrier thatalso contains the external contact device, then it is situated both onthe internal contact terminal and on the external contact terminal.

In a further embodiment, the metallic layer is deposited for the firsttime as described above prior to producing the electrical connection andis then deposited again after producing the electrical connection. It isthus situated on at least the internal contact terminal and envelops atleast one of the contact terminals connected to the wire and also thewire itself.

Further embodiments of the present invention are formed by combinationsof the embodiments described above.

Another embodiment of the connection arrangement according to theinvention provides an additional layer made of hard,high-temperature-resistant plastic above the internal contact terminalconnected to the wire, which additional layer is applied in a particularembodiment of the method according to the invention and brings aboutadditional mechanical stabilization of the contact.

Power semiconductor modules such as IGBT modules, for example, areprovided in a particular manner for the semiconductor circuitarrangement, but the selection is not restricted thereto.

Various carrier substrates, multichip modules, housing forms and alsoother semiconductor circuit arrangements (chip-to-chip bonding) may beused as external contact device.

By way of example, Al and Au wires and in a particular embodiment Cuwires, too, may be used as wire for producing the electrical connectionbetween the semiconductor circuit arrangement and the external contactdevice. However, other materials are also possible. The wire 6 may inthis case have a round or polygonal cross section. Therefore, a “wire”is to be understood for example also to mean a strip or the like.

The metallic layer may be deposited in electroless fashion or in anelectrodeposition process. For electroless coating, it is necessaryfirstly to wet the surface with wetting seeds that settle on all theexposed metallic surfaces. The metallic layer made of NiP or NiB is thendeposited in electroless fashion at the locations where the wetting tookplace. No layer is deposited on nonmetallic surfaces, such as, forexample, the passivation of the semiconductor circuit arrangement.Furthermore, a passivation layer comprising Pd or Au may be deposited onthe metallic layer.

When an electrodeposition process is used, wetting is obviated sincethere is no need to seed the surface to be coated. In this case, themetallic layer is deposited only on metallic surfaces which have aspecific electrical potential. Further advantages are the possibility ofdepositing other metals as well, such as e.g. Cu, Sn, SnAg, Ag and Au,and of obtaining higher deposition rates in the process. Since thisdeposition is effected with current flow, it is important that there isan electrical connection between the semiconductor circuit arrangementand the external contact device.

A method for producing the metallic layer according to the invention issimple and easy to integrate into the process for producing thesemiconductor circuit arrangement at the wafer level or into the overallmounting process of the semiconductor circuit arrangement and thusreplaces costly or complicated alternative methods such as, for example,stabilization of the bonding contact with a plastic coating oroptimization of the metallization on the surface of the semiconductorcircuit arrangement and the parameters of the bonding process.

FIG. 1 illustrates a conventional connection arrangement. Asemiconductor circuit arrangement 1 has a top side 11 and an underside12. An external contact device 3 has a top side 31. The semiconductorcircuit arrangement 1 is fixed on the external contact device 3 by meansof a connecting layer 2 in such a way that the underside 12 of thesemiconductor circuit arrangement 1 and the top side 31 of the externalcontact device 3 are opposite one another. An internal contact terminal4 is situated on the surface of the top side 11 of the semiconductorcircuit arrangement 1, and an external contact terminal 5 is arranged onthe surface of the top side 31 of the external contact device 3. In thiscase, that region of the external contact device 3 which is situatedbelow the semiconductor circuit arrangement 1 and that region of theexternal contact device 3 on which the external contact device 5 issituated are electrically insulated from one another and may even bemechanically separated from one another. The electrical connectionbetween the internal contact terminal 4 and the external contactterminal 5 is produced by means of a wire 6 made, for example, of Al orAu or Cu. The wire 6 may be connected to the contact terminals 4 and 5by means of a wedge-wedge or ball-wedge method.

FIG. 2 then illustrates a connection arrangement according to theinvention. In FIG. 2A, a metallic layer 7 envelops the still exposedsurfaces of the internal and external contact terminals 4 and 5connected to the wire 6 and also the wire 6.

The layer 7 comprises for example Zn seeds 71, an Ni alloy layer 72, inparticular NiP or NiB, and optionally a Pd layer 73 and/or an Au layer74 (cf. detail A in FIG. 2A). In other words: the layer 7 may forexample comprise an Ni alloy layer 72, an Ni alloy layer 72 and a Pdlayer 73, an Ni alloy layer 72 and an Au layer 74 or an Ni alloy layer72, a Pd layer 73 and an Au layer 74.

In FIG. 2B, the metallic layer 7 is applied on the internal and theexternal contact terminal 4 and 5. In another embodiment (notillustrated), the metallic layer 7 is applied only on the internalcontact terminal 4, the wire 6 having a diameter of at least 500 μm orcomprising Cu.

The metallic layer 7 may, however, also be applied on the internal andexternal contact terminals 4 and 5 and additionally on the still exposedsurfaces of the internal and external contact terminals 4 and 5connected to the wire 6 and also on the wire 6, as illustrated in FIG.2A. Such connection arrangement is illustrated in FIG. 2C, the secondmetallic layer being designated by 7′ and being identical inconstruction to the first metallic layer 7. It is likewise possible (butnot illustrated here) for the metallic layer 7 to be situated on theinternal contact terminal 4 and additionally on the still exposedsurfaces of the internal and external contact terminals 4 and 5connected to the wire 6 and also on the wire 6, as illustrated in FIG.2A.

A further embodiment is illustrated in FIG. 2D, where the metallic layer7 is situated on the internal and external contact terminals 4 and 5 asin the exemplary embodiment of FIG. 2B and an additional layer 8 made ofhard, high-temperature-resistant (Tmelting>200° C.) plastic is alsoapplied on the internal contact terminal 4 connected to the wire 6. In afurther embodiment (not illustrated here), the metallic layer 7 isapplied only on the internal contact terminal 4 and the internal contactterminal 4 connected to the wire is additionally enveloped with a layer8 made of a plastic described above.

FIG. 3 schematically illustrates method sequences for producing theconnection arrangements illustrated in FIG. 2. A process 41 involvesapplying the metallic layer 7 and a process 42 involves forming theelectrical connection between the semiconductor circuit arrangement 1and the external contact device 3 by means of the wire 6.

When an electroless deposition method is used, process 41 is subdividedinto the following subprocesses:

A Immersion in a wetting bath and deposition of seeds on all the exposedmetal surfaces,

B Immersion in a bath comprising an Ni alloy and deposition of an Nialloy layer, in particular NiP or NiB, and optionally

C Immersion in a Pd and/or Au bath and deposition of a Pd layer or an Aulayer or a Pd layer and an Au layer.

The wetting bath generally contains Zn, which serves as a seed for theNi alloy deposition, in particular NiP or NiB. If the metallization ofthe contact terminals comprises Nu, then Pd serves as a seed for thelater NiP or NiB deposition. The thickness of the deposited NiP or NiBlayer lies in the range of 0.1 to 100 μm, a typical thickness being 1 to5 μm. The phosphorus content in NiP is typically 5 to 10% and the boroncontent in NiB is typically 1 to 5%. The optional layer made of Pd or Auor the layer system made of Pd and Au is thin in comparison with the NiPor NiB layer. The thickness of the Pd or the Au layer is typically 20 to400 nm and the thickness of an additional Au layer on a Pd layer istypically 40 to 80 nm. The optional layer or the layer system passivatesthe surface of the NiP or NiB layer, prevents the oxidation thereof andimproves the bondability.

The layer 7 thus comprises for example Zn seeds 72, an Ni alloy layer 72and optionally a Pd layer 73 and/or an Au layer 74 (cf. detail A in FIG.2A).

The deposition of the metallic layer may be carried out after thesingulation of the semiconductor circuit arrangement and mounting on theexternal contact device and also prior to singulation in the waferassembly.

When an electrodeposition process is used in process 41, subprocess A isobviated since there is no need to seed the surface to be coated.Further advantages are the possibility of depositing other metals aswell, such as e.g. Cu, Sn, Ag, SnAg and Au, and of obtaining higherdeposition rates in the process.

Process 42 comprises producing the electrical connection between thesemiconductor circuit arrangement 1 and the external contact device 3 bymeans of the wire 6.

FIG. 3A illustrates a first embodiment of the method for producing aconnection arrangement according to the invention, in which firstly theelectrical connection is produced by means of the wire 6 and then themetallic layer 7 is applied. In this case, the process parameters may bechosen such that great deformation of the wire 6 on the internal contactterminal 4 does not occur, which increases the process yield and avoidsdamage in the metallization of the semiconductor circuit arrangement 1.The required reliability of the electrical connection is achieved bymeans of the additional metallic layer 7. A connection arrangement asillustrated in FIG. 2A is obtained as a result.

FIG. 3B illustrates a second embodiment of the method according to theinvention for producing a connection arrangement, in which, aftermounting the semiconductor circuit arrangement 1 on the external contactdevice 3, firstly the metallic layer 7 is applied and then theelectrical connection is produced by means of the wire 6. In this case,the process parameters may be chosen such that a large bearing area ofthe wire 6 on the internal contact terminal 4 occurs, which increasesthe reliability without reducing the process yield and without causingdamage in the metallization of the semiconductor circuit arrangement 1.A connection arrangement as illustrated in FIG. 2B is obtained as aresult.

FIG. 3C illustrates a third embodiment of the method according to theinvention for producing a connection arrangement, in which the metalliclayer 7 is applied both prior to producing the electrical connectionbetween the semiconductor circuit arrangement 1 and the external contactdevice 3 and afterward. In this case, the process parameters may bechosen such that a large bearing area of the wire 6 on the internalcontact terminal 4 occurs, which increases the reliability withoutreducing the process yield and without causing damage in themetallization of the semiconductor circuit arrangement. The secondmetallic layer 7′ on the contacts and the wire 6 itself stabilizes theelectrical connection again and increases reliability further. Aconnection arrangement as illustrated in FIG. 2C is obtained as aresult.

FIG. 3D illustrates a further embodiment, in which, after the processsequence as explained in the second embodiment, the electricalconnection on the internal contact terminal 4 is mechanically stabilizedby the application of the layer 8 made of hard,high-temperature-resistant plastic in the process 43 and the reliabilityis thus increased further. A connection arrangement as illustrated inFIG. 2D is obtained as a result.

FIG. 4 illustrates a perspective illustration of a finished mountedsemiconductor circuit arrangement 1 using the connection arrangementaccording to the invention. In this case, the internal contact terminals4 on the top side 11 of the semiconductor circuit arrangement 1 are ineach case connected to the external contact terminals 5 on the top side31 of the external contact device 3 by means of a wire 6. In accordancewith an exemplary embodiment of the connection arrangement according tothe invention, an additional metallic layer 7 is situated on thesurfaces of the contact terminals 4 and 5 that are still exposed afterthe production of the connection by means of wire 6, and also on thewires 6 (cf. FIG. 2A).

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

1. A connection arrangement between a semiconductor circuit arrangementand an external contact device, comprising: a semiconductor circuitarrangement having a top side and an underside opposite the top side; anexternal contact device having a top side; an electrical connectionbetween an internal contact terminal on the top side of thesemiconductor circuit arrangement and an external contact terminal onthe top side of the external contact device comprises an electricallyconductive wire; wherein a first metallic layer is arranged on a surfaceof the internal contact terminal and a second metallic layer is arrangedon a surface of the wire, and the first and second metallic layerscomprises a material selected from a group consisting of Cu or anarbitrary Ni compound, NiP, NiB, NiMo or NiRe, or tertiary materialcompositions NiPX, where X may be Cu, W, Sn, Mo or Sb.
 2. Thearrangement of claim 1, wherein an additional layer, which comprises Pdand/or Au is provided on the metallic layer.
 3. The arrangement of claim1, where an additional layer made of hard, high-temperature-resistantplastic is applied on the metallic layer above the internal contactterminal connected to the wire on the top side of the semiconductorcircuit arrangement.
 4. The arrangement of claim 1, wherein the wirecomprises Al or Au.
 5. The arrangement of claim 1, wherein the metalliclayer is arranged on the surface of the external contact terminal.